1. Field of the Invention
The present invention relates generally to a fluid-filled cylindrical elastic mount adapted to damp and/or isolate an input vibrational load, based on flows of a fluid in a fluid chamber, and more particularly to such a fluid-filled elastic mount which is simple in construction and which exhibits excellent vibration isolating characteristics with respect to high-frequency vibrations.
2. Discussion of the Prior Art
A cylindrical elastic mount such as a suspension bushing or engine mount used on an automotive vehicle is known for elastically connecting two members in a vibration system in a vibration damping or isolating manner, or for elastically mounting one of the two members on the other member such that the above one member is supported by the other member in a vibration damping or isolating manner. Such a cylindrical elastic mount has an inner and an outer sleeve which are disposed in coaxial or non-coaxial, mutually radially spaced-apart relationship with each other, and an elastic body which elastically connects the inner and outer sleeves. A suitable shaft member fixed to the above one member is fixedly inserted through the inner sleeve, while the other member as a support member is fitted on the outer sleeve. Thus, the elastic mount is interposed between the support member and the shaft member, so that input vibrations applied between these two members are damped and/or isolated based on elastic deformation of the elastic body of the elastic mount.
Since a rubber material is used as the elastic body in such a cylindrical elastic mount as described above, the elastic mount suffers from a potential drawback that the rubber elastic body exhibits an excessively high degree of stiffness due to its resonance upon application of vibrations having relatively high frequencies.
The resonance of the elastic body usually occurs when the frequency of the input vibrations falls within a range of about 300-700 Hz, where the cylindrical elastic mount is used as an engine mount for mounting an engine unit on a front-engine front-drive vehicle (FF vehicle), for example. Thus, the booming noises such as engine-transmitted noises, and other high-frequency vibrations cannot be sufficiently isolated by the elastic mount. In view of the recent increasing requirement for improved noise isolation and driving comfort of the motor vehicles, in particular, there has been a growing need for improving the vibration isolating characteristics of the elastic mount with respect to the high-frequency vibrations applied thereto.